The proposed research will concentrate on genetic interactions between avian RNA tumor viruses. Conditional and nonconditional viral mutants will be studied with the aid of defining viral gene functions which are responsible for neoplastic transformation. The possibility that the viral genome is organized in segments of functionally related genes will be explored and correlated with observations which suggest that the viral RNA consists of and is synthesized in physically distinct subunits. Viral genes active in "normal" avian cells will be characterized by immunological and biochemical tests for viral gene products and by the ability of the resident viral genes to complement known viral mutants. The hypothesis that cellular genes are incorporated into the genome of RNA tumor viruses and play a role in virus induced transformation will also be examined.